This invention relates to sealant compositions and sealant articles and, more particularly, to compositions for sealing discontinuities, for example of the type found in motor vehicles, and to articles used in sealing the discontinuities, as well as to methods of sealing the discontinuities.
Motor vehicles such as, for example, automobiles and trucks have metal joints and seams that must be sealed. One example is a generally non-planar overlap joint formed by welding together two panels (e.g., the roof and the side panel) of the vehicle, such as that often used in motor vehicles to create the U-shaped trough or channel called a roof ditch. One purpose of the roof ditch is to collect and drain water away from the sides of the vehicle.
To prevent water from seeping through the overlap joint formed in the U-shaped trough, it is necessary to seal the joint. It is often difficult to obtain a good seal, because the joint is overlapping and not planar. In addition, the width of the roof ditch typically varies along its length, further complicating the ability to provide a good seal. A variety of materials have been used to seal roof ditch joints, as well as sealants to fill voids in motor vehicles and to block the passage of dirt, moisture, and other undesirable substances.
Sealants have been supplied as liquid or solid materials depending upon the requirements of the particular application. In the automotive industry, for instance, roof ditch joints have been sealed using a paste-like plastisol which is then painted, baked and cooled to room temperature. Hot melt sealants have also been used and are generally solid thermoplastic materials which quickly melt with heating and then form a firm bond upon cooling. In use, a bead of molten liquid sealant is applied on the joint or seam, much in the way caulking is applied. A worker then brushes or levels the material. Applying such a sealant properly takes skill and, because of human error, often results in a poorly sealed joint or seam. Such hot melt sealants are undesirable for visible applications due to their non-uniform appearance. A typical hot melt sealant composition utilizes polyolefins that can be difficult to paint and which have poor adhesion to non-porous metallic surfaces, such as steel and aluminum.
Recently there has been a trend towards more xe2x80x9cuser-friendlyxe2x80x9d polyvinyl chloride-based sealants that are provided in the form of a rope or a tape. The sealants in such a form are disclosed in Japanese National Publication (Kohyo) No. 9-505335. The handling properties of these sealant materials permit faster installation and eliminate the need to finesse the material after application.
Once the sealant has been applied, its exposed surface may be covered with a plastic or rubber article (for example, a molding, cap, etc.) having a flexible top surface, which article may be painted, for example to match or complement the color of the vehicle exterior. Alternatively, the exposed surface of the sealant may be covered with a metal article. The article is typically attached to the sealant surface using a mechanical fastener or a pressure sensitive adhesive.
During its life, the motor vehicle may be exposed to very cold temperatures of xe2x88x9220xc2x0 C. or lower, for example, xe2x88x9230 to xe2x88x9240xc2x0 C., especially if the vehicle is destined for use in extreme northern climates. Prior sealants that are used under such severely cold conditions, particularly those that may be used in roof ditch applications, have been known to exhibit defects such as, for example, cracking, breaking, delaminating or lifting up from the surface to which it has been applied resulting from stresses caused by ordinary vehicle use. Such a defect in the sealant not only permits the intrusion of dirt, moisture, and other undesirable substances but can cause a subsequently applied article (e.g., a molding, cap, etc.) to become loose.
Therefore, a need exists for a solution to the problems described above. In particular, for example, there is a need for a sealant composition and a sealant article capable of effectively sealing discontinuities while remaining flexible enough at lower temperatures to survive the stresses encountered while in use and, thereby, prevent the intrusion of dirt, moisture, and other undesirable substances through the seal.
According to one aspect of the present invention, there is provided a sealant composition comprising a curable epoxy-containing material; a thermoplastic polyamide component having a melting point lower than a curing temperature of the epoxy-containing material; and a curative for the epoxy-containing material; wherein elongation at xe2x88x9220xc2x0 C. becomes at least 2% as a result of curing of the epoxy-containing material.
In one preferred embodiment of the present invention, the sealant composition according to the present invention comprises 10-60% by weight of the epoxy-containing material and 30-70% by weight of the thermoplastic polyamide component.
According to another aspect of the present invention, there is also provided a sealant article comprising a formed sealant layer of a sealant composition of the present invention (hereinafter also referred to as a xe2x80x9cfirst layerxe2x80x9d).
In another preferred embodiment of the present invention, the sealant article according to the present invention is provided with an adhesive layer (hereinafter also referred to as a xe2x80x9csecond layerxe2x80x9d) on one surface of the sealant layer (first layer). The second layer (that is, the adhesive layer) preferably comprises a plurality of adhesive microspheres.
In still another embodiment of the present invention, the surface of the second layer having an adhesive property is provided with a release layer on which a plurality of protrusions are formed, and the protrusions are at least in contact with the second layer.
In a further embodiment of the present invention, a flexible layer (hereinafter also referred to as a xe2x80x9cthird layerxe2x80x9d) is further provided on the sealant layer. Being flexible, the third layer may be disposed at any position, for example, it may be disposed in the sealant layer. Alternatively, it may be attached to the other surface of the sealant layer (i.e. the surface opposite the second layer).